An inode, in a UNIX-based filesystem, is a data structure used to store information, such as metadata, about a file, whereas data blocks are structures used to store the actual data for the file. The information contained in an inode may include ownership of the file, access permission for the file, size of the file, file type and references to locations on disk of the data blocks for the file. The references to the locations of the file data are provided by pointers in the inode, which may further reference indirect blocks that, in turn, reference data blocks, depending on the quantity of data in the file. Changes to the inodes and data blocks are made “in-place” in accordance with the write in-place file system. If an update to a file extends the quantity of data for the file, an additional data block is allocated and the appropriate inode is updated to reference that data block.
The storage of multiple versions of a file can take up a lot of precious storage space. Conventionally, each versions of the file is stored separately.